Saturday, August 28, 2010

(more) Test humor

Sometimes when you're testing things, you have to come up with an "innovative" fixture.  This website really appeals to that part of my career.

Monday, August 23, 2010

Out of my jurisdiction

I spent some time the last couple of weeks researching large scale chip-level testing.  I needed some information for a new project, so I dug around online.

I'm no stranger to wafer-level testing or semiconductor issues - I've been doing that for many years now.  But after digesting the information I found on , I have to say two things.  One, the test issues those guys face are out of my current jurisdiction.  Two, it's pretty cool stuff (see also here) and I'm enjoying learning more about it.

If you want to do some more digging on your own, I would suggest starting with Chip Scale Review and spread out from there.  Also, take a look at this definition of automated test patterns as well as the interface language some large test systems use.

"Today, my jurisdiction ends here. Pick up my hat."

Wednesday, August 18, 2010

I want a tricorder

Android Tricorder App

Last year I compiled a list of tools all test engineers should have.  That list came to mind a couple of months ago when I got my spiffy Droid Incredible phone and downloaded the Tricorder app.  It's a VERY cool tool/toy, especially for a test engineer.

I was reminded of that list again when I read the "New Age of DMMs" article in Evaluation Engineering.  The title implied to me that there was a new line of DMMs I didn't know about.  Sadly, it didn't deliver on that promise - I already knew about PXI DMM cards and the new capabilities they had.

But what about new handheld DMMs?  So I checked out Fluke (of course), and they have a couple of neat multimeters I hadn't seen before.  The Fluke 289 is a good DMM that has logging capability with a TI-calculator-type graphing option (it got a Best In Test award in 2009). Even better, the Fluke 233 has a slick wireless option - you can hook it up, put the display in your pocket, walk up to 30 feet away and still read what it's measuring.
Fluke 289

 Fluke 233 Remote Display Multimeter
Fluke 233

Both of those would be nice to have.  But I still want a tricorder.

Friday, August 13, 2010

Testing rebound

There was an article on Test & Measurement World last week that points out how the major test equipment manufacturers (Agilent, Tektronix, Fluke, etc.) are rebounding from the last year or two.  I would think that this means that test engineering as a career is rebounding as well, since if companies are buying the equipment, then there are engineers needed to spec it, set it up, and run it.  This rebound syncs well with the up-tick I've personally seen in job openings in the Boston area.  Food for thought.

Wednesday, August 4, 2010

LabVIEW 2010? Not quite yet...

I feel sort of bad for picking on National Instruments, after what I've written the past couple months (here or here).  But I'm annoyed and need to vent.

NI released LabVIEW 2010 this week.  I received an email saying that, "for immediate access, download your new software online at the Services Resource Center."  I had a new computer running Windows 7, so I decided to try the 64-bit version of the new software.  The download and install took several hours but appeared to work fine.

Problems occurred, however, when I tried to open one of my projects.  As soon as I opened the top level VI, LabVIEW started requesting subVIs from toolkits that I had a right to have - database toolkit, report generation, etc. - but were not installed with the download.  So I called NI support and they suggested downloading the toolkits individually.

No luck.  NONE of the toolkits are 64-bit (except I think vision), therefore none of them will work with my 64-bit install.  NI is working on it, but it isn't there yet.  When I asked the NI support guy if all the time I spent downloading, installing, and setting up was therefore wasted, he just said, "that is a true statement."

Sunday, August 1, 2010

Misleading specifications

I've been learning more about solar cell testing over the past year.  I have a couple of test systems I'm developing, I've taken data, and it's been interesting.  It's also been frustrating.

As an example let's consider I-V sweeping, the bread and butter of semiconductor testing.  Most of the basic values of a solar cell can be determined from a quick IV check.  One of those values, the short circuit current (Isc), helps determine the maximum power a cell could theoretically produce.  A high Isc is nice to have.

When I first looked at measuring IVs for solar cells last year, I tried to re-purpose my National Instruments PXI chassis to this task.  I knew that the source measure unit (SMU) in the chassis (PXI-4130) could only go up to about 1A, but there was an auxiliary supply that could plug right in to the SMU: the PXI-4130 Power SMU.  On the NI page for the aux the output specs are listed at "12 VDC, up to 5 A, up to 60 W, 0 to 55 °C" (note the "5A" limit).  So I bought the aux supply and got started testing.

But as I tested larger and better cells, with more total current output, I ran into limitations with the NI approach.  I couldn't measure an Isc above 2 amps.  This confused me somewhat, since I had seen the the five amp limit on the NI page.  Adding insult to injury, I didn't even need the SMU to output that current - the solar cell was generating the current.  

I then considered connecting multiple SMUs.  There is a "knowledge base" article on the NI website that supposedly answers the question, "What is the Maximum Voltage and Current that the NI DC Power Supplies can Source when Cascading Outputs?"  But nowhere on that page does it list a maximum current.  I even found a Photovoltaic Solar Cell I-V Characterization Bundle page that says you can "add more SMUs to get three times the voltage or current."  I struggled with this problem for a month.  

Well, I finally got an answer from NI last week.  The SMU cannot measure above 2A current because the PXI chassis has to dissipate the power, regardless of where the current source is.  The chassis has "a hard limit on the amount of power consumed by each of the SMUs."  In other words, National Instruments has some cleaning to do on their website.


So what's the moral of this rant?  First, I'm going to get a different power supply (maybe Agilent).  Second, you cannot always trust the hardware verbage you read online.